Pin a feed to the top of the feed list

subscriptions.pinned, per person, set by PATCH /api/feeds/{id} {pinned} and
returned as FeedRow.pinned. Kept out of Sub, which the scanner merges into its
policy; set_subscription names its columns, so saving a feed's settings leaves
the pin alone (tested).

Pinned feeds come first in the list, a pin before the name and a rule under the
block: a pinned folder with its feeds under it, a feed from inside one lifted out
of it. The pin button is on both the feed and the folder page.

Closes #33.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web/index.html

@@ -363,6 +363,10 @@ input:focus,select:focus{outline:0;border-color:var(--accent)}
 .feed.sel{background:var(--raise)}
 /* A show sits under its folder's title, a size down, so an open folder reads as one. */
 .feed.child{margin-left:11px}
+/* Pinned feeds, at the top of the list: a small pin before the name, and a rule under the last. */
+.feed .fpin .i{width:10px;height:10px;margin-right:5px;vertical-align:-1px;color:var(--accent)}
+.feed.lastpin{margin-bottom:9px}
+.feed.lastpin::after{content:"";position:absolute;left:8px;right:8px;bottom:-5px;border-bottom:1px solid var(--line)}
 .feed.child .art{width:28px;height:28px;font-size:11px}
 /* Only a folder has a triangle, hung in the margin so every feed's art lines up with the places
    above it. The button is the row's full height and 24 px wide: a near miss used to open the